Tropical Storms (SQA National 5 Geography): Revision Note

Distribution of Tropical Storms

Features of tropical storms

• Tropical storms are large, intense low-pressure systems (between 100–1000km across and pressure below 950mb)

• Depending on their wind speed, they are:

  • Tropical depressions – wind speeds of less than 62 km/h (38 mph)

  • Tropical storms – wind speeds ranging from 63 to 118 km/h (39 to 73 mph)

  • Tropical cyclones – wind speeds of 119 km/h (74 mph) and above

• Tropical cyclones are also known as hurricanes or typhoons, depending on their location

• Characteristics include:

  • Heavy rainfall

  • High wind speeds 

  • High waves and storm surges

• The rotating clouds surround a calm eye in the centre 

Distribution

• Tropical storms develop in tropical regions between 5° and 30° north and south of the equator

• They form over warm ocean water

Formation of Tropical Storms

• Tropical storms require specific conditions to form:

  • Warm sea surface temperatures (over 27°C)

  • Deep ocean (at least 50–60m deep)

  • Low wind shear

  • Moist air

  • Low air pressure 

Stages of tropical storm formation

• There are several stages in the formation of a tropical storm:

  • Warm, moist air rises quickly, forming an area of intense low pressure

  • Air from high-pressure areas rushes in to take the place of the rising air, generating strong winds

  • This air then rises, forming a continuous flow of rising air

  • As the air rises, it cools and condenses, releasing heat energy which helps to power the storm

  • Air at the top of the storm goes outwards away from the centre of the storm

  • The rising air spirals around the centre due to the spinning of the Earth on its axis

  • Some of the air sinks at the centre, creating a calm area known as the eye of the storm

  • Tropical storms will die out if the heat energy and moisture from the ocean are no longer available to drive the storm